• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.673-678
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• 2014

In a compressor, highly impulsive pressure fluctuations induced by a reciprocating piston and valves cause noise and vibration to be so critical issues that low noise requirement always challenges engineers developing it. A muffler is frequently used for reducing these impulsive noise components, but has adverse effects on compressor's performance due to additional pressure drop and heat transfer of refrigerant when it pass through the muffler. In this study, compressible full 3-dimensional CFD simulations are performed to investigate both of flow and acoustic performances of a muffler in use for compressors. On a basis of the analysis results, a parametric study using design factors introduced to improve flow and acoustic performances of the existing muffler is carried out. Finally, improved designs are suggested to confirm the current results.

• 실천공학교육논문지
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• 제9권2호
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• pp.91-98
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• 2017

To produce highly creative students, engineering education must develop both problem recognition skills and the ability to solve problems independently. Chonnam National University has been developing a creativity program in which students identify and solve problems themselves. Initially, the primary focus was on solving problems, but this was unsuccessful at attracting the students' interest. To overcome this, we adopted Csikszentmihalyi's flow theory in our creativity program, much like the way this theory is used in computer games. As a result of adopting flow theory, we achieved our goal. Thus, in this paper, we will introduce Chonnam National University's creativity program (designed based on flow theory), which we will call the Self-Directed Creativity-Upgrade Program. Furthermore, we will discuss the impact of this program based on statistical analyses.

• 대한기계학회논문집B
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• 제37권3호
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• pp.285-292
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• 2013

본 연구의 목적은 평판의 선단에 설치된 트리핑 와이어에 의한 경계층 박리가 층류에서 난류로의 천이에 미치는 영향과 그 결과로 발생하는 물질전달에 미치는 영향을 규명하는 것이다. 나프탈렌승화법을 사용하여 평판에서의 국소물질전달계수를 측정하였으며, 유동 경계층의 효과를 평가하기 위해 발달된 유동과 발달하는 유동의 조건에서 트리핑 와이어가 설치된 평판에서의 국소물질전달계수를 설치되지 않은 평판에서의 값과 비교하였다. 발달하는 유동에서 국소물질전달계수가 변화하는 경향은 트리핑 와이어가 설치된 평판과 설치되지 않은 평판이 비슷하지만 발달된 유동에서는 상당히 다르게 나타났다. 평균 Sherwood 수는 경계층 박리로 인하여 트리핑와이어가 설치된 평판이 설치되지 않은 평판에 비해서 훨씬 높았다.

• 한국전산유체공학회지
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• 제13권1호
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• pp.21-27
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• 2008

A numerical study for laminar flow in the entrance region of helical tubes for uniform inlet velocity conditions is carried out by means of the finite volume method to investigate the effects of Reynolds number, pitch and curvature ratio on the flow development. This results cover a curvature ratio range of 1/10$\sim$1/320, a pitch range of 0.0$\sim$3.2, and a Reynolds number range of 125$\sim$2000. It has been found that the curvature ratio does significantly effect on the angle of flow development, but the pitch and Reynolds number do not. The characteristic angle $\phi_c(=\phi/\sqrt{\delta})$, or the non-dimensional length $\overline{l}(=l\sqrt{\delta}cos(atan\lambda)/d)$ can be used to represent the flow development for uniform inlet velocity conditions. In uniform inlet velocity conditions, the growth of boundary layer delays the flow development attributed to centrifugal force, and in which conditions the amplitude of flow oscillations is smaller than that in parabolic inlet velocity conditions. If the pitch increases or if the curvature ratio or Reynolds number decreases, the minimum friction factor and the fully developed average friction factor normalized with the friction factor of a straight tube and the flow oscillations decrease.

• Journal of Advanced Marine Engineering and Technology
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• 제21권2호
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• pp.126-135
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• 1997

Drag reduction in polymer solutions is the phenomenon where by extremely dilute solutions of high molecular weight polymers exhibit frictional resistance to flow much lower than the pure solvent. This effect, largely unexplained as yet, has attracted the attention of polymer scientists and fluid flow specialists. Although applications are beginning to appear, the principle interest to data has been in attempting to relate the effect to the fluid mechanics of turbulent flow. Drag reduction in two phase flow can be applied to the transport of crude oil, phase change system such as chemical reactor, and pool and boiling flow. But the research on drag reduction in two phase flow is not intensively investigated. Therefore, experimental investigations have been carried out to analyze the drag reduction produced by polymer addition in the single phase and two phase flow system. The objectives of the proposed investigation are primarily in identifying and developing high performance polymer additives for fluid transportations with the benefits of turbulent drag. Also we want to is to evaluate the drag reduction in horizontal flow by measuring pressure drop and mean velocity. Experimental results show higher drag reduction using co - polymer(A611P) then using polyacrylamide (PAAM) and faster degradation using PAAM than using A611P under the same superficial velocity.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2006년도 추계학술대회 논문집
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• pp.131-134
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• 2006

Whole flow fields of a room air conditioner (RAC) have been visualized by a Particle Image Velocimetry (PIV) technique to analyze the flow structure by various inlet and outlet angles, and to control an eccentric vortex which affects an efficiency and noise of the RAC. A test model with 5 stages of a cross flow fan has been manufactured and a transparent acryl has been installed at the side of the test model for the PIV experiment. The inlet and outlet flows and the flow inside the cross flow fan have been analyzed by varying the inlet grill angles and outlet blade angles. The movement of the eccentric vortex has been investigated experimentally by developing the measurement technique for the inner flow field of the cross flow fan, and the relationship between the control of the eccentric vortex and the inlet and outlet angles has been confirmed in this study.

• 설비공학논문집
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• 제16권10호
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• pp.895-900
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• 2004

With the phaseout of CFC and HCFC refrigerants, refrigeration and heat pump systems must be redesigned to match and improve system performance with alternative refrigerants. A generalized flow model for predicting mass flow rate through short tube orifices is derived from a power law form of dimensionless parameters generated by Pi-theorem. The database for developing the correlation includes extensive experimental data for R12, R22, R134a, R407C, R410A, and R502 from the open literature. The correlation yields an average deviation of $0.3\%$ and a standard deviation of $6.1\%$ based on the present database. In addition, rating charts for predicting refrigerant flow rate through short tube orifices are generated for R12, R22, R134a, R407C, R410A, and R502.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 추계 학술대회논문집
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• pp.188-193
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• 1995

Incompressible developing entry flows through square ducts with 90 degree bends are studied numerically by using an efficient implicit SMAC scheme with different boundary conditions. This study eventually aimed at passage flow analysis of turbomachinery elements with a strong curvature such as centrifugal impeller or draft tube. The generalized implicit scheme used in the present study has been developted to solve the three-dimensional Navier-Stokes equations by the author. Numerical results for some different numerical conditions are obtained and compared with each other

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.17-18
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• 2003

Drop deformation in a cylindrical contraction geometry, characterized here by the formation of a thread of drop fluid in the contraction, is predicted using a Volume-of-Fluid numerical technique. The predicted drop shape is found to closely follow the observed deformation. A capillary instability in the developing drop thread in the contraction was predicted, in agreement with experimental observation.

• 산업경영시스템학회지
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• 제14권23호
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• pp.65-70
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• 1991

This paper is concerned with a flow-shop scheduling problem for all jobs having the common due date using V-Shape penalty cost function for earliness and lateness. The objective of the paper is to develop an efficient heuristic scheduling algorithm for minimizing total penalty cost function and for determining the optimal common due date. In addition, the between-job-delay for two machines are considered for developing the algorithm. A numerical example is given for illustrating the proposed algorithm.